Supermarket giants Sainsbury’s and Tesco sales have jumped as the fall in grocery inflation slowed slightly last month.

Inflation fell to 6.8%, from 6.9% in December, as retailers took their “foot off the promotions gas slightly” after Christmas, according to Kantar head of retail and consumer insight Fraser McKevitt.

However, grocery sales grew 2.9% by value over the four weeks to 21 January.

Sainsbury’s led the pack of traditional grocers with sales increasing by 8.1% in the 12 weeks to 21 January, as its market share jumped 0.3% from last year to 15.7%. Tesco also grew sales by 6.3% as its share edged up 0.1% to 27.6%.

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Lidl was once again the fastest growing grocer in Britain for the fifth month in a row and was the only supermarket to see a double digit growth in the last 12 weeks.

Spending at the discounter surged 11.9%, with a market share of 7.5%, while fellow discounter Aldi’s sales jumped 7.2%.

McKevitt said: “All eyes are back on inflation again, after the Consumer Prices Index’s (CPI) unexpected jump earlier in the month.

“There’s been a lot of speculation about the impact the Red Sea shipping crisis might have on the cost of goods, but the story in the grocery aisles this January is more about the battle between the supermarkets to offer best value, rather than geopolitics.”